Figure 5. Reduction of I_K1 in HF under AP-clamp.

The inward rectifier K⁺ current (I_K1) was measured as Ba²⁺ (100 μM)-sensitive current in HF and age-matched control cells. AP-clamp using a prerecorded typical AP (shown above) was applied at 2 Hz. (A–C) I_K1 traces (mean±SEM) recorded under preserved [Ca²⁺]_i cycling (Physiol), [Ca²⁺]_i buffering (BAPTA_i) and CaMKII inhibition using AIP. I_K1 was significantly reduced in HF in all these conditions. (D–F) Statistics for peak I_K1 density shows that the reduction is not influenced by [Ca²⁺]_i buffering or acute CaMKII inhibition. (E) I_K1 density measured at the mid-plateau of the AP was also reduced. (F) Net charges carried by I_K1 was further reduced in HF when measured with [Ca²⁺]_i buffering. Columns and bars represent mean±SEM. n refers to cells/animals measured in each group. ANOVA with Bonferroni posttest, *p<0.05, **p<0.01, ***p<0.001.